Duplicating the old images

Hi,

   This is the new environment. One Appliance in Primary site and one in DR site. I started taking Backups from Sep 1st week to primary Appliance and replicating to DR Appliance with retention 2 months in both sites.

   Now i want to duplicate all old images in Primary site from Disk to Tape and keep retention for four months. Future duplication it can be done through SLP. But how to duplicate old images which i have from Sep to Tapes?

Should i do using bpduplicate or vault? This is one time process. Can you all help me in your suggestions?

Thanks,

Anushi